1. Field of the Invention
The present invention is directed to a transmission that is used, for example, in the drivetrain of a vehicle for transmitting torque between a drive unit, e.g., an internal combustion engine, and the driven wheels in order to adapt the gear ratio to different driving states. For example, a gear unit of this kind can be constructed as an automatic transmission or as an automated shift transmission, i.e., as basically automatic or self-shifting.
2. Related Art
FIG. 1 shows a portion of a drivetrain, designated generally by 10, of a vehicle. This portion comprises a hydrodynamic torque converter 12 and an automatic transmission 14 downstream thereof in the torque path.
A housing 16 of the torque converter 12 is formed for coupling to a driveshaft 18, i.e., for example, a crankshaft of an internal combustion engine, and carries an impeller 20. Arranged in the interior of the housing 16 is a turbine 22, which is coupled, for example by toothed engagement, via a turbine hub, not shown, or a driven hub in general, to a transmission input shaft, designated generally by 24, so as to rotate jointly around an axis of rotation A. Further, a stator, designated generally by 26, is arranged in the interior of the housing 16 and is mounted so as to be rotatable in one direction around the axis of rotation A on a supporting hollow shaft 30 supported at a transmission housing 28.
The transmission input shaft 24 is rotatably supported at the transmission housing 28, for example, at a housing wall 32 thereof. A transmission output shaft 36 is rotatably supported at another housing wall 34 at a distance axially from housing wall 32. A gear ratio changing system, designated generally by 38, is located in the torque path between the transmission input shaft 24 and the transmission output shaft 36. In the illustrated example of an automatic transmission, this gear ratio changing system 38 comprises a plurality of planetary gear stages 40, brakes 42 and clutches 44. By controlling or activating/deactivating the brakes 42 and clutches 44, the torque path via the various planetary gear stages 40 and consequently the gear ratio between the transmission input shaft 24 and the transmission output shaft 36 can be varied.
A torsional vibration damping arrangement, designated generally by 48, is arranged in the torque converter 12 in the torque path between a lockup clutch 46 and the driven hub or transmission input shaft 24. This torsional vibration damping arrangement 48 has an input region 50, which is provided, for example, by the output portion of the lockup clutch 46, and an output region 52, which is also coupled to the turbine 22 and which, for example, also provides the driven hub. Two parallel torque transmission paths 54, 56 are formed between the input region 50 and the output region 52. These two parallel torque transmission paths 54, 56 split in the input region 56 and converge again in the region of a coupling arrangement designated generally by 58. As a result, the torque components that are transmitted along the two torque transmission paths 54, 56, and that comprise the torque which is to be transmitted and is received at the input region 50, are brought together in the coupling arrangement 58 and received at the output region 52. A first torque transmission path 54 of the two torque transmission paths 54, 56 comprises a phase shifter arrangement 60. The phase shifter arrangement 60 is formed with a vibration system 62, which comprises a primary side 64 formed, for example, with two cover disk elements, a secondary side 66 formed with a central disk element, and a spring arrangement 68. The primary side 64 and the secondary side 66 can rotate relative to one another around the axis of rotation against the return force of the spring arrangement, for example, a plurality of helical compression springs that are distributed in circumferential direction and which can be supported at the primary side 64 and secondary side.
When there are rotational irregularities or torsional vibrations in the torque to be transmitted, vibrations are excited in the vibration system 62 of the phase shifter arrangement 60. Provided this excitation of vibrations takes place at a frequency below the natural frequency of the vibration system 62, the vibration system 62 operates subcritically, meaning that the excitation of vibrations and the reaction of the vibration system 62 are in phase with one another. When the excitation frequency or vibration frequency exceeds the natural frequency of the vibration system 62, this vibration system 62 passes into a supercritical state in which a phase shift is produced between excitation and reaction, which ideally can be a maximum of 180° so that the reaction, i.e., the vibration of the secondary side 66, is essentially 180° out of phase with the excitation, i.e., with the vibration of the primary side 64.
Due to the fact that the torque to be transmitted is divided into two torque transmission paths 54, 56, torque components containing vibrations or rotational irregularities are transmitted via these two torque transmission paths 54, 56. Since the second torque transmission path 56 in the illustrated example has no phase shifter arrangement but rather is, for example, comparatively rigid, i.e., cannot vibrate resonantly in the range of the occurring excitation frequencies, the torque components transmitted via the two torque transmission paths 54, 56 can, as was already mentioned, be shifted in phase relative to one another ideally by a maximum of 180° with respect to the vibrations contained therein. When these two torque components converge in the coupling arrangement 58, these out-of-phase vibration components are superposed on one another such that, ideally, these vibration components cancel each other out virtually completely due to the mutual phase shift. The torque that is sent on to the output region 52 then substantially contains no more vibration components or appreciably fewer vibration components and is conveyed onward in this manner to the rest of the drivetrain, in this case the transmission input shaft 24 and transmission 14.
The coupling arrangement 58 comprises a planetary gear arrangement 70 with a planet wheel carrier 72 provided in the second torque transmission path 56. This planet wheel carrier 72 carries a plurality of planet wheels 74 that are distributed in a circumferential direction. Each planet wheel 74 cooperates with a drive-side ring gear 76 provided in the first torque transmission path 54 at the secondary side 66 of the vibration system 62 and with a driven-side ring gear 78, which is provided at the output region 52 and which is also, for example, coupled with the turbine 22 so as to be fixed with respect to rotation relative to it. For this purpose, the planet wheels 74 can be formed with toothed areas. The gear ratio that can be achieved in the coupling arrangement 58 can be adjusted through the configuration of the planet wheels 74 and ring gears 76, 78, respectively. A gear ratio of 1 results when both ring gears 76, 78 are substantially identical with respect to their toothing and diameter such that the two toothed regions of the planet wheels 74 associated with the ring gears 76, 78 can be provided, for example, by a continuous toothing. However, a gear ratio of 1 means that the entire torque is transmitted via the first torque transmission path 54 and, therefore, no phase shift is generated that can be used for a canceling superposition of vibrations. When the gear ratio has a value other than 1, depending on whether this value is greater than or less than 1, the torque component transmitted via the two torque transmission paths 54, 56 is adjusted and the above-mentioned superposition of vibration components with at least partial cancelation can accordingly be achieved. A gear ratio other than 1 such as this can be achieved, for example, in that the ring gears 76 and 78 have different addendum modifications while the toothed regions of the planet wheels 74 have the same configuration. Also, the toothed regions provided at the planet wheels 74 and associated with the ring gears 76, 78 have different diameters, which, of course, necessitates a correspondingly different diameter of the ring gears 76, 78 with respect to one another and results in a gear ratio other than 1.